Slender Monorail Beam

[J1D]

We have a monorail for a couple of tons lifting capacity. The beam is S250x35 the span is about 18ft, the maximumn slenderness ratio is therefore 240+/- (no lateral bracing other than at the ends). The design engineer ignored the ratio and simply considered it as a beam.

Can someone advise if there is a concern for the typical limit of 200? Can monorail be treated as beam-column as well since there is 25% impact load (axial foce).

Thanks in advance.

 

[JStephen]

If I understand your post right, you have a beam spanning over a horizontal distance, but are trying to apply column slenderness ratios to it. The column slenderness ratios don't directly apply to it unless it is somehow loaded in compression rather than bending. In AISC ASD or AISC LRFD, there are equations and charts for load capacity or allowable stress for different lengths of unstiffened beams, and those are what you need to refer to.

If this is a column supporting the crane, then refer to the column design formulas or charts in the above. See the commentary for effective length guidelines.

 

[UcfSE]

Note that the slenderness limit of 200 is a recommendation, not a requirement, as noted in the AISC (USA). If you are using a different design code, there may be a similar clause or even one more strict. The catch is that if you exceed a slenderness of 200, then you're on your own as far as whether the design equations work. When you go past the slenderness recommendations in the code, some of the assumptions used to derive those equations become less valid.

If you are concerned, you might try talking to your supervisor or the engineer who did the design.

 

[civilperson]

The beam mentioned seems close to a S10x25.4, with the loads and span given in the original text and assuming horizontal alignment of the beam gives allowable stress of 12.7 KSI. The maximum load of two ton will cause flexural bending stresses of 8.7 KSI times whatever impact factor you impose. Seems sufficient for impact factor of 33%-45%.